The present invention relates to an emulsion of silver halide (hereinafter silver halide is also referred to as "AgX") which is useful in the field of photography. More particularly, the present invention relates to a silver halide emulsion which is excellent in sensitivity, image quality and pressure properties. The present invention also relates to a silver halide lightsensitive material using the same.
The spectral sensitization, sharpness, light scattering performance, covering power, rate of development, graininess, etc. are improved as compared with those of the lightsensitive material using nontabular silver halide grains, when tabular silver halide emulsion grains are used in a photographic lightsensitive material. Therefore, tabular grains having mutually parallel twin planes and having hexagonal principal planes composed of {111} faces (hereinafter referred to as "{111} tabular grains") are now often used.
These grains are described in detail in, for example, Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 58-113926, JP-A-58-113927, JP-A-58-113928, JP-A-2-828, JP-A-2-28638 and JP-A-2-298935.
However, when a large amount of a spectral sensitizing dye is adsorbed on silver halide grains, grains having {100} faces exhibit spectral sensitization performance more desirable than that of grains having {111} faces. This tendency is manifest from a comparison of cubic grains having principal planes composed of {100} faces to octahedral grains having principal planes composed of {111} faces. Therefore, there is a demand for the development of tabular grains having principal planes composed of {100} faces (hereinafter referred to as {100} tabular grains) which replace the conventionally employed {111} tabular grains.
Although reports on {100} tabular grains having principal planes shaped into a right angled parallelogram are a few, such tabular grains are described in, for example, JP-A-51-88017 and Jpn. Pat. Appln. KOKOKU Publication No. (hereinafter referred to as JP-B-) 64-8323.
A. MIGNOT, E. FRANCOIS AND M. CATINAT, "CRISTAUX DE BROMURE D'ARGENT PLATS, LIMITES PAR DES FACES {100} ET NON MACLES", Journal of Crystal Growth 123 (1974) 207-213 reports an observation of tabular silver bromide crystals composed of {100} faces having square or rectangular principal planes.
As disclosed in U.S. Pat. No. 4,063,951, tabular grains defined by {100} crystal faces are formed from monodispersed seed grains, and tabular grains having an average aspect ratio of 1.5 to 7 are produced by ripening in the presence of ammonia. On the other hand, U.S. Pat. No. 4,386,156 discloses a process for producing a tabular silver bromide emulsion having an average aspect ratio of at least 8, in which seed grains are ripened in the absence of nonhalide silver ion completing agents.
The inventor incorporated a tabular emulsion having principal planes composed of {100} crystal faces in a lightsensitive material and evaluated the performance of the lightsensitive material. When a pressure was applied to the lightsensitive material, the occurrence of fog (called "stress marks" in the art of photography) was observed to which a complaint for compensation would be laid on the market.
The inventor has studied a technology for overcoming the stress marks and has completed the present invention.